1. FIELD OF THE INVENTION
This invention relates to the art of cleaning contamination from surfaces such as old paint, grease or rust, through the use of a blast of sodium bicarbonate particles transported into impact engagement with the surface by a stream of pressurized air or water.
2. SUMMARY OF PRIOR ART
In recent years, there has been an increase in use of cleaning systems utilizing a blast of sodium bicarbonate particles suspended in a stream of pressured air or water. Sodium bicarbonate has distinct advantages over sand particles used for many years for similar purposes. Because of the toxic nature of sand particles when inhaled, government regulations require the use of sophisticated fresh air breathing masks to insure that the operator will not be filling his lung with silica products. For the same reason, sand blasting cannot be economically utilized to clean machines in food processing plants because of the difficulty of removing the silica particles from wherever they fall, and particularly from bearings.
In contrast, sodium bicarbonate particles are reasonably soluble in water and can be readily removed by hosing down the machine after the blast cleaning. Sodium bicarbonate is not toxic and does not require elaborate fresh air breathing masks for the operator. Only standard protective clothing and ear and eye protection may be utilized but this is not necessarily a requirement but depends primarily on the substrate and the coating being removed. Sodium bicarbonate can be utilized to remove surface corrosion, lime, scale, paint, grease and machine oil from any surface, without damaging the surface.
The employment of sodium bicarbonate as a blast type cleaning medium does encounter problems in effecting the transfer of sodium bicarbonate particles from a supply hopper to the nozzle from which the pressured water or air is issued and where the sodium bicarbonate is mixed into the pressured fluid. The method and apparatus heretofore employed followed the pattern of apparatus utilized for sand blasting in that a high air pressure was maintained on the top of the mass of sodium bicarbonate particles disposed in the supply hopper. The reason for the high pressure was that the particles normally had to be introduced into the high pressure air or water blasting stream, thus requiring that a higher pressure be maintained above the mass of sodium bicarbonate particles to effect the feeding of a desired quantity per unit of time to the nozzle. Under these conditions, the sodium bicarbonate particles have been found to not feed uniformly and consistently into the stream of pressured air or water. Moreover, the performance of such prior art apparatus was highly dependent on the particular size of sodium bicarbonate particles being utilized as a blasting medium.
In an attempt to overcome these particle delivery problems, a sodium bicarbonate crystal has been developed and marketed under the trademark "ARMEX" by the Church & Dwight Co., Inc., of Princeton, N.J. A flow additive is applied to the sodium bicarbonate particles to promote the flow of the resulting crystals from the hopper and into the pressured stream of air or water passing through the discharge nozzle.
Even this improved particle form of sodium bicarbonate which, of course, is more expensive than untreated sodium bicarbonate particles, still suffered from clogging and/or inconsistent rates of delivery of the sodium bicarbonate particles to the pressurized fluid stream.
There is a need, therefore, for an improved method and apparatus for effecting blast cleaning through the utilization of sodium bicarbonate particles, whether treated with a flow promotion agent or not, which will effect a more reliable and consistent delivery of such particles to the blast nozzle and which can be conveniently adjusted to accommodate a substantial range of particle sizes of sodium bicarbonate.